Cardiac mapping instrument with shapeable electrode

ABSTRACT

An instrument including an elongated shaft and a non-conductive handle is disclosed. The shaft defines a proximal section and a distal section. The distal section forms an electrically conductive tip. Further, the shaft is adapted to be transitionable from a straight state to a first bent state. The shaft is capable of independently maintaining the distinct shapes associated with the straight state and the first bent state. The handle is rigidly coupled to the proximal section of the shaft. The instrument is useful for epicardial pacing and/or mapping of the heart for temporary pacing on a beating heart, for optimizing the placement of ventricular leads for the treatment of patients with congestive heart failure and ventricular dysynchrony and/or for use in surgical ablation procedures.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 10/056,807 filed Jan. 25, 2002, the disclosure ofwhich is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This invention relates to methods and systems for epicardialpacing and mapping of the heart for temporary pacing on a beating heart,for optimizing the placement of ventricular leads for the treatment ofpatients with congestive heart failure and ventricular dysynchrony orfor use in surgical ablation procedures. More particularly, it relatesto a mapping instrument designed to be indifferent to rotationalorientation and including a bendable shaft capable of independentlymaintaining a desired shape.

BACKGROUND OF THE INVENTION

[0003] The heart includes a number of pathways that are responsible forthe propagation of signals necessary to produce continuous, synchronizedcontractions. Each contraction cycle begins in the right atrium where asinoatrial node initiates an electrical impulse. This impulse thenspreads across the right atrium to the left atrium, stimulating theatria to contract. The chain reaction continues from the atria to theventricles by passing through a pathway known as the atrioventricular(AV) node or junction, which acts as an electrical gateway to theventricles. The AV junction delivers the signal to the ventricles whilealso slowing it, so the atria can relax before the ventricles contract.

[0004] Disturbances in the heart's electrical system may lead to variousrhythmic problems that can cause the heart to beat irregularly, too fastor too slow. Irregular heart beats, or arrhythmia, are caused byphysiological or pathological disturbances in the discharge ofelectrical impulses from the sinoatrial node, in the transmission of thesignal through the heart tissue, or spontaneous, unexpected electricalsignals generated within the heart. One type of arrhythmia istachycardia, which is an abnormal rapidity of heart action. There areseveral different forms of atrial tachycardia, including atrialfibrillation and atrial flutter. With atrial fibrillation, instead of asingle beat, numerous electrical impulses are generated by depolarizingtissue at one or more locations in the atria (or possibly otherlocations). These unexpected electrical impulses produce irregular,often rapid heartbeats in the atrial muscles and ventricles. Patientsexperiencing atrial fibrillation may suffer from fatigue, activityintolerance, dizziness and even strokes.

[0005] The precise cause of atrial fibrillation, and in particular thedepolarizing tissue causing “extra” electrical signals, is currentlyunknown. As to the location of the depolarizing tissue, it is generallyagreed that the undesired electrical impulses often originate in theleft atrial region of the heart. Recent studies have expanded upon thisgeneral understanding, suggesting that nearly 90% of these “focaltriggers” or electrical impulses are generated in one (or more) of thefour pulmonary veins (PV) extending from the left atrium. In thisregard, as the heart develops from an embryotic stage, left atriumtissue may grow or extend a short distance into one or more of the PVs.It has been postulated that this tissue may spontaneously depolarize,resulting in an unexpected electrical impulse(s) propagating into theleft atrium and along the various electrical pathways of the heart.

[0006] A variety of different atrial fibrillation treatment techniquesare available, including drugs, surgery, implants, and ablation. Whiledrugs may be the treatment of choice for some patients, drugs typicallyonly mask the symptoms and do not cure the underlying cause. Implantabledevices, on the other hand, usually correct an arrhythmia only after itoccurs. Surgical and ablation treatments, in contrast, can actually curethe problem by removing and/or ablating the abnormal tissue or accessorypathway responsible for the atrial fibrillation. The ablation treatmentsrely on the application of various destructive energy sources to thetarget tissue, including direct current electrical energy,radiofrequency electrical energy, laser energy, microwave energy,ultrasound energy, thermal energy, and the like. The energy source, suchas an ablating electrode, is normally disposed along a distal portion ofa catheter or instrument. Ablation of the abnormal tissue or accessorypathway responsible for atrial fibrillation has proven highly viable.

[0007] Regardless of the application, ablation of tissue is generallyachieved by applying the destructive energy source to the target tissue.For some treatments, an ablating element can be formed as a part of acatheter that is delivered via the vascular system to the target site.While relatively non-invasive, catheter-based treatments present certainobstacles to achieving precisely located, complete ablation lesionpatterns due to the highly flexible nature of the catheter itself, theconfines of the surgical site, etc.

[0008] A highly viable alternative device is the hand-heldelectrosurgical instrument. As used herein, the term “electrosurgicalinstrument” includes a hand-held instrument capable of ablating tissueor cauterizing tissue, but does not include a catheter-based device. Theinstrument is relatively short (as compared to a catheter-based device),and rigidly couples the electrode tip to the instrument's handle that isotherwise held and manipulated by the surgeon. The rigid construction ofthe electrosurgical instrument requires direct, open access to thetargeted tissue. Thus, for treatment of atrial fibrillation via anelectrosurgical instrument, it is desirable to gain access to thepatient's heart through one or more openings in the patient's chest(such as a sternotomy, a thoracotomy, a small incision and/or a port).In addition, the patient's heart may be opened through one or moreincisions, thereby allowing access to the endocardial surface of theheart.

[0009] Once the target site (e.g., right atrium, left atrium, epicardialsurface, endocardial surface, etc.) is accessible, the surgeon positionsthe electrode tip of the electrosurgical instrument at the target site.The tip is then energized, ablating (or for some applications,cauterizing) the contacted tissue. A desired lesion pattern is thencreated (e.g., portions of a known “Maze” procedure) by moving the tipin a desired fashion along the target site. In this regard, the surgeoncan easily control positioning and movement of the tip, as theelectrosurgical instrument is rigidly constructed and relatively short(in contrast to a catheter-based ablation technique).

[0010] Ablation of PV tissue may cause the PV to shrink or constrict dueto the relatively small thickness of tissue formed within a PV. BecausePV's have a relatively small diameter, a stenosis may result due to theablation procedure. Even further, other vital bodily structures aredirectly adjacent each PV. These structures may be undesirably damagedwhen ablating within a PV. Therefore, a technique has been suggestedwhereby a continuous ablation lesion pattern is formed in the leftatrium wall about the ostium associated with the PV in question. Inother words, the PV is electrically isolated from the left atrium byforming an ablation lesion pattern that surrounds the PV ostium. As aresult, any undesired electrical impulse generated within the PV wouldnot propagate into the left atrium, thereby eliminating unexpected atriacontraction.

[0011] Electrosurgical instruments, especially those used for thetreatment of atrial fibrillation, have evolved to include additionalfeatures that provide improved results for particular procedures. Forexample, U.S. Pat. No. 5,897,553, the teachings of which areincorporated herein by reference, describes a fluid-assistedelectrosurgical instrument that delivers a conductive solution to thetarget site in conjunction with electrical energy, thereby creating a“virtual” electrode. The virtual electrode technique has proven highlyeffective in achieving desired ablation while minimizing collateraltissue damage. Other electrosurgical instrument advancements havelikewise optimized system performance. However, a common characteristicassociated with available electrosurgical instruments is a “designed-in”directional orientation. That is to say, electrosurgical devices, andespecially those used for atrial fibrillation treatment procedures, arecurved along a length thereof, as exemplified by the electrosurgicalinstrument of U.S. Pat. No. 5,897,553. In theory, this permanent curvedfeature facilitates the particular procedure (or lesion pattern) forwhich the electrosurgical instrument is intended. Unfortunately,however, the actual lesion pattern formation technique and/or bodilystructure may vary from what is expected, so that the curve is less thanoptimal. Additionally, the pre-made curve may be well suited for oneportion of a particular procedure (e.g., right atrium ablation patternduring the Maze procedure), but entirely inapplicable to another portion(e.g., left atrium ablation during the Maze procedure). As a result, theelectrosurgical instrument design may actually impede convenient use bya surgeon.

[0012] Electrosurgical instruments continue to be highly useful forperforming a variety of surgical procedures, including surgicaltreatment of atrial fibrillation. While certain advancements haveimproved overall performance, the accepted practice of imparting apermanent curve or other shape variation into the instrument itself mayimpede optimal usage during a particular procedure. Therefore, a needexists for an electrosurgical instrument that, as initially presented toa surgeon, is indifferent to rotational orientation, and further iscapable of independently maintaining a number of different shapes asdesired by the surgeon.

[0013] In cases of atrial fibrillation, it is desirable to identify theorigination point of the undesired electrical impulses prior toablation. Mapping may be accomplished by placing one or more mappingelectrodes into contact with the tissue in question. Mapping of tissuemay occur by placing one or more mapping electrodes into contact withthe endocardial surface of the heart and/or the epicardial surface ofthe heart. Therefore, a need exists for a mapping instrument that iscapable of mapping the heart, e.g., during an ablation procedure.Preferably, this mapping instrument, as initially presented to asurgeon, would be indifferent to rotational orientation, and furtherwould be capable of independently maintaining a number of differentshapes as desired by the surgeon.

[0014] As used herein, the term “mapping instrument” includes ahand-held instrument capable of pacing and/or mapping cardiac tissue.The mapping instrument is similar to the electrosurgical instrumentdescribed above in that it is relatively short (as compared to acatheter-based device), and rigidly couples an electrode tip to theinstrument's handle that is otherwise held and manipulated by thesurgeon. The rigid construction of the mapping instrument requiresdirect, open access to the targeted tissue. Thus, for mapping and/orpacing of cardiac tissue via the mapping instrument, it is desirable togain access to the patient's heart through one or more openings in thepatient's chest (such as a stemotomy, a thoracotomy, a small incisionand/or a port). In addition, the patient's heart may be opened throughone or more incisions, thereby allowing access to the endocardialsurface of the heart.

[0015] Once the target site (e.g., right atrium, left atrium, rightventricle, left ventricle, epicardial surface, endocardial surface,pulmonary veins, etc.) is accessible, the surgeon positions theelectrode tip of the mapping instrument at the target site. The surgeoncan easily control positioning and movement of the tip, as the mappinginstrument is rigidly constructed and relatively short (in contrast to acatheter-based technique).

[0016] In cardiac resynchronization therapy (CRT) for the treatment ofpatients with congestive heart failure and ventricular dysynchrony, theheart is paced from both ventricles simultaneously by placing twoventricular leads on opposite sides of the heart. Various studies haveshown that lead location can affect cardiac function; therefore,optimizing placement of the left ventricular lead on the leftventricular free wall may improve CRT results and patient outcomes.

[0017] Venous anatomy may not allow a transvenous lead to be placed inan optimal location. However, an epicardial lead may be placed at anysite on the heart, creating the opportunity to optimize lead position.There are several situations during implantation of a left ventricularlead in which one should consider converting from a transvenous leadprocedure to an epicardial lead procedure. These include inability tocannulate the coronary sinus or the desired coronary vein, inability ofthe lead to properly lodge in the vein or lack of any vein in thepreferred location.

[0018] Interest in optimizing left ventricular lead placement forcardiac resynchronization therapy is being supported by growing datathat demonstrate the location of the lead on the heart can affecthemodynamics and improve patient outcomes. Epicardial mapping is atechnique to determine a patient-specific location for the left-sidedpacing lead in CRT procedures.

SUMMARY OF THE INVENTION

[0019] One aspect of the present invention relates to a system forablating cardiac tissue comprising an electrosurgical instrument and amapping instrument. The electrosurgical instrument includes an elongatedshaft and a non-conductive handle. The shaft defines a proximal section,a distal section, and an internal lumen extending from the proximalsection. The distal section forms an electrically conductive rounded tipand defines at least one passage fluidly connected to the lumen. Thispassage distributes fluid from the internal lumen outwardly from theshaft. Further, the shaft is adapted to be transitionable from astraight state to a bent state, preferably a number of different bentstates. In this regard, the shaft is capable of independentlymaintaining the distinct shapes associated with the straight state andthe bent state(s). The non-conductive handle is rigidly coupled to theproximal section of the shaft. With this in mind, an exterior surface ofthe shaft distal the handle and proximal the distal section iselectrically non-conductive. In one preferred embodiment, the shaft iscomprised of an elongated electrode body and an electrical insulator.The electrode body defines the distal section and is rigidly coupled tothe handle. The electrical insulator surrounds at least a portion of theelectrode body proximal the distal section such that the tip is exposed.

[0020] During use, and when first presented to a surgeon, the shaft isin the straight state such that the electrosurgical instrument iseffectively indifferent to a rotational orientation when the handle isgrasped by the surgeon. Subsequently, the surgeon can bend the shaft toa desired shape (i.e., the bent state) being most useful for theparticular electrosurgical procedure. During the procedure, a conductivefluid is directed onto the target site from the internal lumen via thepassage. The tip then energizes the dispensed fluid, causing tissueablation or cauterization.

[0021] The mapping instrument also includes an elongated shaft and anon-conductive handle. The shaft defines a proximal section and a distalsection. The distal section forms an electrically conductive roundedtip. Like the electrosurgical instrument, the shaft of the mappinginstrument is adapted to be transitionable from a straight state to abent state, preferably a number of different bent states. In thisregard, the shaft is capable of independently maintaining the distinctshapes associated with the straight state and the bent state(s). Thenon-conductive handle is rigidly coupled to the proximal section of theshaft. With this in mind, an exterior surface of the shaft distal thehandle and proximal the distal section is electrically non-conductive.In one preferred embodiment, the shaft is comprised of an elongatedelectrode body and an electrical insulator. The electrode body definesthe distal section and is rigidly coupled to the handle. The electricalinsulator surrounds at least a portion of the electrode body proximalthe distal section such that the tip is exposed.

[0022] During use, and when first presented to a surgeon, the shaft isin the straight state such that the mapping instrument is effectivelyindifferent to a rotational orientation when the handle is grasped bythe surgeon. Subsequently, the surgeon can bend the shaft to a desiredshape (i.e., the bent state) being most useful for the particularmedical procedure.

[0023] Yet another aspect of the present invention relates to anablation system including an electrosurgical instrument, a source ofconductive fluid, an energy source and a mapping instrument. Theelectrosurgical instrument includes an elongated shaft and anon-conductive handle. The shaft defines a proximal section, a distalsection, and an internal lumen extending from the proximal section. Thedistal section forms an electrically conductive rounded tip and definesat least one passage fluidly connected to the lumen. Further, the shaftis adapted to be transitionable from, and independently maintain a shapein, a straight state and a bent state. The handle is rigidly coupled tothe proximal section of the shaft. An exterior surface of the shaftdistal the handle and proximal the distal section is electricallynon-conductive. The source of conductive fluid is fluidly connected tothe internal lumen. Finally, the energy source is electrically connectedto the tip. During use, the electrosurgical instrument can be presentedto the target site in either the straight state or the bent state.Regardless, the shaft independently maintains the shape associated withthe selected state. Conductive fluid is delivered from the conductivefluid source to the internal lumen, and is then distributed to thetarget site via the passage. The energy source is activated, therebyenergizing the electrode tip. This action, in turn, energizes thedistributed conductive fluid, causing desired tissue ablation orcauterization. In one preferred embodiment, the electrosurgical systemfurther includes an indifferent, or non-ablating, electrode (such as agrounding patch). The indifferent electrode is electrically connected tothe energy source and it is placed separately from the target site. Forexample, the indifferent electrode may be placed on the back of thepatient. The mapping instrument also includes an elongated shaft and anon-conductive handle. The shaft defines a proximal section and a distalsection. The distal section forms an electrically conductive roundedtip. Further, the shaft is adapted to be transitionable from, andindependently maintain a shape in, a straight state and a bent state.The handle is rigidly coupled to the proximal section of the shaft. Anexterior surface of the shaft distal the handle and proximal the distalsection is electrically non-conductive. Finally, the energy source iselectrically connected to the tip. During use, the mapping instrumentcan be presented to the target site in either the straight state or thebent state. Regardless, the shaft independently maintains the shapeassociated with the selected state. The energy source is activated,thereby energizing the electrode tip. This action, in turn, causesdesired tissue to be stimulated. In one preferred embodiment, theelectrosurgical system further includes an indifferent, or non-ablating,electrode (such as a needle electrode). The indifferent electrode iselectrically connected to the energy source and it is placed separatelyfrom the target site.

[0024] Yet another aspect of the present invention relates to a methodof performing an electrosurgical procedure. The method includesproviding an electrosurgical instrument and a mapping instrument bothincluding an elongated shaft and, a handle. In this regard, the shaft ofthe electrosurgical instrument defines a proximal section, a distalsection, and an internal lumen. The proximal section is rigidly coupledto the handle, whereas the distal section forms a round tip. Finally,the internal lumen extends from the proximal section and is in fluidcommunication with at least one passage formed in the distal section. Anexterior surface of the shaft distal the handle and proximal the distalsection is electrically non-conductive. The shaft is provided in aninitial straight state that otherwise defines a linear axis. The shaftis then bent to a first bent state in which a portion of the shaft isdeflected relative to the linear axis. In this regard, the shaftindependently maintains a shape of the first bent state. The shaft ofthe mapping instrument defines a proximal section and a distal section.The proximal section is rigidly coupled to the handle, whereas thedistal section forms a round tip. An exterior surface of the shaftdistal the handle and proximal the distal section is electricallynon-conductive. The shaft is provided in an initial straight state thatotherwise defines a linear axis. The shaft is then bent to a first bentstate in which a portion of the shaft is deflected relative to thelinear axis. In this regard, the shaft independently maintains a shapeof the first bent state. The tip of the electrosurgical instrument ispositioned at a tissue target site. In one preferred embodiment, anindifferent electrode is placed in contact with the patient. Conductivefluid is dispensed from the passage to the tissue target site via theinternal lumen. Finally, energy is applied to the dispensed fluid byenergizing the tip. Subsequently, the energized tip and conductive fluidablates or cauterizes tissue at the tissue target site. In oneembodiment, the tissue target site comprises tissue of a patient'sheart, and the method further includes accessing the tissue target sitethrough one or more openings in the patient's chest. In anotherembodiment, after a first lesion pattern is formed at a first tissuetarget site, the shaft is bent to a second shape and the procedurerepeated to effectuate a second lesion pattern at a second tissue targetsite. In one embodiment, the tip of the mapping is positioned at atissue target site comprising tissue of a patient's heart, and themethod further includes accessing the tissue target site through one ormore openings in the patient's chest.

[0025] Yet another aspect of the present invention relates to a methodof performing an electrosurgical procedure. The method comprisesproviding an instrument having an elongated shaft and a handle, theshaft defining a proximal section rigidly coupled to the handle, adistal section forming an electrically conductive tip; positioning thetip through a patient's chest; applying ablation energy to the tip whilecontacting cardiac tissue; creating an ablation lesion to isolate anarea of cardiac tissue; stopping the application of ablation energy tothe tip; repositioning the tip; and applying stimulation energy to thetip while contacting the area of isolated cardiac tissue to assesstransmurality of the ablation lesion. The method further comprises aninternal lumen extending from the proximal section of the shaft and influid communication with at least one passage formed in the distalsection of the shaft. Conductive fluid is dispensed from the internallumen of the shaft via the at least one passage while applying ablationenergy to the tip. In one embodiment, the ablation energy isradiofrequency energy.

[0026] Yet another aspect of the present invention relates to a methodof performing a left sided epicardial lead placement procedure. Themethod comprises providing an instrument including an elongated shaftand a handle, the shaft defining a proximal section rigidly coupled tothe handle, a distal section forming an electrically conductive tip;positioning the tip through a patient's chest to contact a first area ofepicardial tissue of the patient's left ventricle; applying stimulationenergy to the patient's right ventricle; recording the time at which adepolarization wave is sensed over the left ventricle followingstimulation of the right ventricle; repositioning the tip to contact asecond area of epicardial tissue of the patient's left ventricle;reapplying stimulation energy to the patient's right ventricle;recording the time at which the depolarization wave is sensed over theleft ventricle following restimulation of the right ventricle; placingan epicardial lead in contact with the area of tissue that had thelongest time interval at which the depolarization wave was sensed overthe left ventricle following stimulation of the right ventricle. Oncethe optimal lead location site has been determined, it can visuallymarked by using adjacent anatomical landmarks. The mapping instrument isremoved and an epicardial pacing lead implanted at that site.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a side view of an electrosurgical system in accordancewith the present invention, including portions shown in block form;

[0028]FIG. 2 is a perspective view of an electrosurgical instrumentportion of the system of FIG. 1, with a handle removed;

[0029]FIG. 3 is an enlarged, cross-sectional view of a portion of anelectrosurgical instrument of FIG. 1 taken along the line 3-3;

[0030]FIG. 4A is an enlarged, perspective view of a distal portion ofthe electrosurgical instrument of FIG. 1;

[0031]FIG. 4B is an enlarged, perspective view of a distal portion of analternative embodiment electrosurgical instrument in accordance with thepresent invention;

[0032]FIGS. 5A-5C are side views of the electrosurgical instrument ofFIG. 1, illustrating exemplary shapes available during use of theelectrosurgical instrument;

[0033]FIG. 6 is an enlarged, side view of a portion of an alternativeembodiment electrosurgical instrument in accordance with the presentinvention;

[0034]FIG. 7A is a cut-away illustration of a patient's heart depictinguse of an electrosurgical instrument in accordance with the presentinvention during a surgical ablation procedure;

[0035]FIG. 7B is an enlarged illustration of a portion of FIG. 7A;

[0036]FIGS. 8A and 8B are side perspective views of an alternativeelectrosurgical instrument in accordance with the present invention;

[0037]FIG. 9A is an enlarged, perspective view of a distal portion of analternative embodiment electrosurgical instrument in accordance with thepresent invention;

[0038]FIG. 9B is an enlarged, transverse, cross-sectional view of theelectrosurgical instrument of FIG. 9A;

[0039]FIG. 9C is an enlarged, longitudinal, cross-sectional view of theelectrosurgical instrument of FIG. 9A;

[0040]FIG. 10A is an enlarged, perspective view of a distal portion ofan alternative embodiment electrosurgical instrument in accordance withthe present invention;

[0041]FIG. 10B is an enlarged, cross-sectional view of theelectrosurgical instrument of FIG. 10A;

[0042]FIG. 10C is an enlarged, perspective view of a distal portion ofan alternative embodiment electrosurgical instrument in accordance withthe present invention;

[0043]FIG. 10D is an enlarged, cross-sectional view of a portion of theelectrosurgical instrument of FIG. 10C;

[0044]FIG. 11 is an enlarged, cross-sectional view of a portion of analternative embodiment electrosurgical instrument in accordance with thepresent invention;

[0045]FIG. 12 is a schematic view illustrating an ablation lesionproduced in accordance with the present invention;

[0046]FIG. 13 is a schematic view illustrating an ablation lesionproduced in accordance with the present invention;

[0047]FIG. 14 is a side view of a mapping system in accordance with thepresent invention, including portions shown in block form;

[0048]FIGS. 15A-15C are side views of the mapping instrument of FIG. 14,illustrating exemplary shapes available during use of the mappinginstrument;

[0049]FIG. 16 is a perspective view of a mapping instrument portion ofthe system of FIG. 14, with a handle removed;

[0050]FIG. 17 is an enlarged, cross-sectional view of a portion of amapping instrument of FIG. 14 taken along the line 17-17;

[0051]FIG. 18 is an enlarged, side view of a portion of an alternativeembodiment of a mapping instrument in accordance with the presentinvention;

[0052]FIG. 19A is a cut-away illustration of a patient's heart depictinguse of a mapping instrument in accordance with the present inventionduring a surgical ablation procedure;

[0053]FIG. 19B is an enlarged illustration of a portion of FIG. 19A;

[0054]FIGS. 20A and 20B are side perspective views of an alternativeembodiment of a mapping instrument in accordance with the presentinvention;

[0055]FIG. 21A is an enlarged, perspective view of a distal portion ofan alternative embodiment of a mapping instrument in accordance with thepresent invention;

[0056]FIG. 21B is an enlarged, transverse, cross-sectional view of themapping instrument of FIG. 21A;

[0057]FIG. 21C is an enlarged, longitudinal, cross-sectional view of themapping instrument of FIG. 21A;

[0058]FIG. 22 is a cut-away illustration of a patient's heart depictingactivation patterns and cell-to-cell conduction from right ventricularpacing;

[0059]FIG. 23 is an illustration of a patient's heart depictingepicardial mapping to optimize left ventricular lead placement;

[0060]FIG. 24 is a schematic of PDI measurement in accordance with oneembodiment of the present invention; and

[0061]FIG. 25 is a schematic of PDI measurement in accordance with oneembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0062] One preferred embodiment of an electrosurgical system 10 inaccordance with the present invention is shown in FIG. 1. The system 10is comprised of an electrosurgical instrument 12, a fluid source 14, apower source 16, and an indifferent electrode 18. The various componentsare described in greater detail below. In general terms, however, thefluid source 14 is fluidly connected to the electrosurgical instrument12. Similarly, the power source 16 is electrically connected to theelectrosurgical instrument 12 and to the indifferent electrode 18.During use, conductive fluid is delivered from the fluid source 14 to adistal portion of the electrosurgical instrument 12. The distributedfluid is energized by the electrosurgical instrument 12 via the powersource 16. The so-energized conductive fluid is capable of forming avirtual electrode, which is capable of ablating or cauterizing contactedtissue.

[0063] The electrosurgical instrument 12 includes a handle 20 and ashaft 22. As described in greater detail below, the shaft 22 is rigidlycoupled to the handle 20, and is transitionable from a straight state(as illustrated in FIG. 1) to a bent state (for example as shown inFIGS. 5B and 5C). In this regard, the shaft 22 independently maintainsthe shape associated with the particular state (i.e., straight or bent).

[0064] The handle 20 is preferably made of a sterilizable, rigid, andnon-conductive material, such as a polymer or ceramic. Suitable polymersinclude rigid plastics, rubbers, acrylics, nylons, polystyrenes,polyvinylchlorides, polycarbonates, polyurethanes, polyethylenes,polypropylenes, polyamides, polyethers, polyesters, polyolefins,polyacrylates, polyisoprenes, fluoropolymers, combinations thereof orthe like. Further, the handle 20 is ergonomically designed tocomfortably rest within a surgeon's hand (not shown). To this end, thehandle 20 may include a grip portion 24 that is circular in crosssection. This configuration facilitates grasping of the handle 20, andthus of the electrosurgical instrument 12, at any position along thegrip portion 24 regardless of an overall rotational orientation of theelectrosurgical instrument 12. That is to say, due to the circular,cross-sectional shape of the grip portion 24, the electrosurgicalinstrument 12 can be rotated to any position relative to a central axisA, and still be conveniently grasped by the surgeon. In an even morepreferred embodiment, the grip portion 24 defines a gradual, distallyincreasing diameter that provides an orientation feature to help asurgeon identify where along the length of the electrosurgicalinstrument 12 he or she is grasping. For example, if the surgeon graspsthe electrosurgical instrument 12 out of his visual sight during amedical procedure, the surgeon may identify based on the grip portion's24 diameter where along the instrument he has grasped. Finally, the gripportion 24 is preferably formed of a low durometer polymer. Suitablepolymers include low durometer plastics, rubbers, silicones, acrylics,nylons, polystyrenes, polyvinylchlorides, polycarbonates, polyurethanes,polyethylenes, polypropylenes, polyamides, polyethers, polyesters,polyolefins, polyacrylates, polyisoprenes, fluoropolymers, combinationsthereof or the like. The grip portion 24 alternatively may be asponge-like or foam-like material, such as an open-cell material or aclosed-cell material.

[0065] Regardless of exact configuration, the handle 20 forms orencompasses one or more central lumens (not shown). The lumen(s)provides a pathway for a line or tubing 26 from the fluid source 14 tothe shaft 22, as well as a pathway for a line or wiring 28 from thepower source 16 to the shaft 22. In this regard, FIG. 2 illustrates theelectrosurgical instrument 12 with the handle 20 removed. The tubing 26from the fluid source 14 (FIG. 1) is shown as extending to, and beingfluidly connected with, the shaft 22. Similarly, the line 28 from thepower source 16 (FIG. 1) is shown as extending to, and beingelectrically connected with, the shaft 22.

[0066] Returning to FIG. 1, the shaft 22 is an elongated, relativelyrigid component defining a proximal section 40 and a distal section 42.The distal section 42 terminates in an electrically conductive tip 44.As described in greater detail below, the tip 44 is rounded, defining auniform radius of curvature. With this configuration, the tip 44 is,similar to the handle 20, indifferent to rotational orientation of theelectrosurgical device 12. That is to say, regardless of how a surgeon(not shown) grasps the handle 20 (i.e., the rotational position of thehandle 20 relative to the central axis A), a profile of the tip 44 inall directions (e.g., in front of the surgeon's thumb position, behindthe surgeon's thumb position, etc.) is always the same so that the tip44 is readily maneuvered along tissue (not shown) in any direction. Tothis end, the rounded shape facilitates sliding movement of the tip 44along the tissue.

[0067] With additional reference to FIG. 3, the shaft 22 defines aninternal lumen 50 that is fluidly connected to the tubing 26. In thisway, the internal lumen 50 delivers fluid from the fluid source 14 tothe distal section 42.

[0068] With additional reference to FIG. 4A, the distal section 42preferably forms a plurality of passages 52 that are fluidly connectedto the internal lumen 50. The passages 52 are formed at or proximal thetip 44 and preferably are uniformly located relative to a circumferenceof the distal section 42. For example, in one preferred embodiment, twosets 54 a, 54 b of the passages 52 are provided, in addition to acentral passage 54 c at the tip 44. The passages 52 associated with eachof the two sets 54 a, 54 b are circumferentially aligned, and uniformlyspaced approximately 90° from one another. For example, in oneembodiment, the passages 52 are uniformly located on a hemisphericalportion of the tip 44 as described below. Alternatively, other numbersand locations are acceptable. By preferably uniformly spacing thepassages 52, however, the distal section 42 is further formed to beindifferent to rotational orientation of the electrosurgical instrument12. In other words, regardless of the rotational position of theelectrosurgical instrument 12 and/or the direction of tip 44 movement,the passages 52 provide a relatively uniform disbursement of conductivefluid about the tip 44 via the internal lumen 50. In an alternativeembodiment, the tip 44 is made of a porous material, that allows fluidto pass from the internal lumen 50 through the tip 44.

[0069] In another alternative embodiment, and as best shown in FIG. 4B,at least some of the passages 52 (for example, the passage set 54 b) arelocated along a generally hemispherical portion 56 of the tip 44. Thisone preferred design facilitates a more complete delivery of liquid to atarget site (not shown) that is otherwise contacted by the tip 44. Ingeneral terms, during an electrosurgical procedure, it is important thata sufficient volume of irrigation fluid is continually provided to theelectrode tip 44/target site tissue interface to reduce the opportunityfor tissue charring or desiccation. Previous electrosurgical designspositioned all of the passages 52 (except for the central passage 54 c)along a cylindrical portion 58 of the tip 44 (as opposed to thegenerally hemispherical portion 56). With this prior design, where aparticular surgical procedure required that the tip 44 be oriented suchthat the passages 52 are “below” the electrode tip 44/target site tissueinterface, some or all of the irrigation liquid otherwise dispensed fromthe passages 52 (other than the central passage 54 c) might flow awayfrom the electrode tip 44 (or back along the shaft 22). The onepreferred passage configuration of FIG. 4B overcomes this concern, asall of the irrigation liquid distributed from the passages 54 b on thegenerally hemispherical portion 56 will be delivered to the electrodetip 44/target site tissue interface due to surface tension at theinterface.

[0070] Regardless of passage location, a further preferred feature ofthe shaft 22 is a malleable or shapeable characteristic. In particular,and with additional reference to FIGS. 5A-5C, the shaft 22 is configuredto be transitionable from an initial straight state (FIG. 5A) to a bentor curved state (FIGS. 5B and 5C). In this regard, the electrosurgicalinstrument 12, and in particular the shaft 22, is initially presented toa surgeon (not shown) in the straight state of FIG. 5A, whereby theshaft 22 assumes a straight shape defining the central axis A. In thestraight state, the shaft 22 is indifferent to rotational orientation,such that the electrosurgical instrument 12 can be grasped at anyrotational position and the tip 44 will be located at an identicalposition. Further, as previously described, a profile of the tip 44 isalso uniform or identical at any rotational position of theelectrosurgical instrument 12. Subsequently, depending upon theconstraints of a particular electrosurgical procedure, the shaft 22 canbe bent relative to the central axis A. Two examples of an applicablebent state or shape are provided in FIGS. 5B and 5C. In a preferredembodiment, the shaft 22 can be bent at any point along a lengththereof, and can be formed to include multiple bends or curves.Regardless, the shaft 22 is configured to independently maintain theshape associated with the selected bent shape. That is to say, the shaft22 does not require additional components (e.g., pull wires, etc.) tomaintain the selected bent shape. Further, the shaft 22 is constructedsuch that a user can readily re-shape the shaft 22 back to the straightstate of FIG. 5A and/or other desired bent configurations. Notably, theshaft 22 is configured to relatively rigidly maintain the selected shapesuch that when a sliding force is imparted onto the shaft 22 as the tip44 dragged across tissue, the shaft 22 will not overtly deflect from theselected shape.

[0071] In one preferred embodiment, the above-described characteristicsof the shaft 22 are achieved by forming the shaft 22 to include anelongated electrode body 60 and an electrical insulator covering 62 asshown in FIGS. 1 and 3. The electrode body 60 defines the proximalsection 40 and the distal section 42 of the shaft 22. To this end, theproximal section 40 of the electrode body 60 is rigidly coupled to thehandle 20. The insulator 62 covers a substantial portion of theelectrode body 60, preferably leaving the distal section 42 exposed. Inparticular, the insulator 62 is positioned to encompass an entirety ofthe electrode body 60 distal the handle 20 and proximal the distalsection 42 (and in particular, proximal the passages 52 and the tip 44).

[0072] In one preferred embodiment, the electrode body 60 is a tubeformed of an electrically conductive, malleable material, preferablystainless steel, however other materials such as, for example, nitinolcan be used. The passages 52 are preferably drilled, machined, lasercut, or otherwise formed through at least a portion of the electrodebody 60. The passages or openings 52 may comprise circular holes,semi-circular holes, oval holes, rectangular slots, and/or otherconfigurations for allowing fluid to pass.

[0073] The insulator 62 is formed of one or more electricallynon-conductive materials, and serves to electrically insulate theencompassed portion of the electrode body 60. Multiple layers ofelectrically non-conductive materials can help prevent the likelihood offorming an electrical short along the length of the electrode body 60due to a mechanical failure of one of the non-conductive materials. Inthis regard, the insulator 62 is preferably comprised of two materialshaving considerably different mechanical properties, e.g., a siliconeand a fluoropolymer. In one preferred embodiment, a silicone tubingmaterial is overlaid with a heat shrink fluoropolymer tubing material.Alternatively, the insulator 62 may be one or more non-conductivecoatings applied over a portion of the electrode body 60. In addition tobeing non-conductive, the insulator 62 is preferably flexible andconforms to the electrode body 60 such that the insulator 62 does notimpede desired shaping and re-shaping of the electrode body 60 aspreviously described.

[0074] It will be understood that the preferred construction of theshaft 22 to include the elongated electrode body 60 and the insulator 62is but one available configuration. Alternatively, the shaft 22 can beconstructed of an electrode material forming the tip 44, and a rigid ormalleable, non-conductive tube rigidly connecting the tip 44 to thehandle 20. The non-conductive tube can include one or more metalconductors, such as straight wire and/or windings for electricallyconnecting the tip 44 to the power source 16. Along these same lines,another alternative embodiment includes forming the tip 44 from aninherently porous material. For example, the tip 44 may comprise one ormore porous polymers, metals, or ceramics. Further, the tip 44 may becoated with non-stick coatings such as PTFE or other types of coatingssuch as biological coatings. Another alternative embodiment includesconstruction of the shaft 22 to include one or more metal conductors,such as straight wire and/or windings inside a rigid or malleablenon-conductive polymer tube. The non-conductive polymer tube includesone or more openings, such as holes, slots or pores (preferablycorresponding with the passages 52 previously described), which allowconductive fluid to exit the polymer tube. The conductive fluid createsa virtual electrode via electrically connecting the one or more metalconductors to the target tissue. Conversely, the shaft 22 may comprise apolymer tube having one or more openings, such as holes, slots or pores(preferably corresponding with the passages 52 previously described),placed inside an electrical conductor, such as a metal tube having oneor more openings, such as holes, slots or pores, or a metal windinghaving a spacing that allows conductive fluid to pass through, tocontrol conductive fluid delivery through the electrical conductor.Finally, the insulator 62 may cover a portion of the metal tube orwindings.

[0075] With respect to the above-described alternative embodiments,connection between the elongated tube and the separate tip 44 can beaccomplished in a variety of manners. Once again, the elongated tube cancomprise a conductive or non-conductive material(s), such as metal(s) orplastic(s). The elongated tube can be connected to the tip 44 via avariety of coupling techniques, including, for example, welding, laserwelding, spin welding, crimping, gluing, soldering and press fitting.Alternatively, the distal end of the elongated tube and the tip 44 canbe configured to threadably engage one another and/or mechanicalengagement member(s) (e.g., pins, screws, rivets, etc.) can be employed.In another embodiment, the elongated tube is rigidly coupled to the tip44. In yet another embodiment, the tip 44 can be moveably coupled to theelongated tube, whereby the tip 44 can be moved and/or locked relativeto the elongated tube. For example, the tip 44 can be coupled to theelongated tube via one or more joints or hinges. The joints or hingescan be ball joints and/or joints that include a pin. To this end, apin-type joint can be configured to allow the tip 44 to swivel relativeto the elongated tube. Further, the joint(s) can be configured to moveand lock into position. In addition, one or more actuators (e.g., knobs,buttons, levers, slides, etc.) can be located on, for example, thehandle 20 (FIG. 1) for actuating the joint(s). With the above in mind,FIG. 6 illustrates a portion of an alternative embodiment shaft 22′including a tip 44′ moveably coupled to an elongated tube 63 by a pin64.

[0076] Returning to FIG. 1, the electrosurgical instrument 12 preferablyincludes a coupling member 65 for rigidly coupling the shaft 22 to thehandle 20. The coupling member 65 can comprise one or more polymers,plastics, and/or rubbers. For example, the coupling member 65 cancomprise one or more silicones, acrylics, nylons, polystyrenes,polyvinylchlorides, polycarbonates, polyurethanes, polyethylenes,polypropylenes, polyamides, polyethers, polyesters, polyolefins,polyacrylates, polyisoprenes, fluoropolymers, combinations thereof orthe like. The coupling member 65 preferably forms a drip edge 66 tointerrupt, divert and prevent any flow of liquid from the tip 44, downthe shaft 22 and onto the handle 20, thereby preventing any electricallyconducting fluid from contacting the surgeon.

[0077] Regardless of exact construction of the electrosurgicalinstrument 12, the fluid source 14 maintains a supply of conductivefluid (not shown), such as an energy-conducting fluid, an ionic fluid, asaline solution, a saturated saline solution, a Ringer's solution, etc.It is preferred that the conductive fluid be sterile. The conductivefluid can further comprise one or more contrast agents, and/orbiological agents such as diagnostic agents, therapeutic agents ordrugs. The biological agents may be found in nature (naturallyoccurring) or may be chemically synthesized.

[0078] As a point of reference, during use the conductive fluid servesto electrically couples the electrode tip 44 of electrosurgicalinstrument 12 to the tissue to be treated, thereby lowering theimpedance at the target site. The conductive fluid may create a largereffective electrode surface. The conductive fluid can help cool the tip44 of the electrosurgical instrument 12. The conductive fluid may keepthe surface temperature of the tip 44 below the threshold for bloodcoagulation, which may clog the electrosurgical instrument 12. Theconductive fluid may also cool the surface of the tissue therebypreventing over heating of the tissue which can cause popping,desiccation, burning and/or charring of the tissue. The burning and/orcharring of the tissue may also clog the electrosurgical instrument 12.Therefore, use of the conductive fluid may reduce the need to remove aclogged electrosurgical instrument for cleaning or replacement. Further,charred tissue has high impedance, thereby making the transfer of RFenergy difficult, and may limit the ability of the electrosurgicalinstrument 12 to form a transmural lesion. The delivery of conductivefluid during the electrosurgical process may help create deeper lesionsthat are more likely to be transmural. Transmurality is achieved whenthe full thickness of the target tissue is ablated. Continuousconductive fluid flow may ensure that a conductive fluid layer betweenthe tip 44 and the contours of the tissue to be treated is created.

[0079] In one preferred embodiment, the fluid source 14 includes a fluidreservoir, such as a bag, a bottle or a canister, for maintaining asupply of conductive fluid previously described. With thisconfiguration, the fluid reservoir can be positioned at an elevatedlocation, thereby gravity feeding the conductive fluid to theelectrosurgical instrument 12, or the fluid reservoir may bepressurized, thereby pressure feeding the conductive fluid to theelectrosurgical instrument 12. For example, a pressure cuff may beplaced around a flexible bag, such as an IV bag, of conductive fluid,thereby pressure feeding the conductive fluid to the electrosurgicalinstrument 12. Alternatively, the fluid source 14 can include, and/or beconnected to, a manual or electrical pump (not shown), such as aninfusion pump, a syringe pump, or a roller pump. The fluid source 14 canfurther comprise one or more orifices or fluid regulators, (e.g.,valves, fluid reservoirs, conduits, lines, tubes and/or hoses) tocontrol flow rates. The conduits, lines, tubes, or hoses may be flexibleor rigid. For example, a flexible hose may be used to communicate fluidfrom the fluid source 14 to the electrosurgical instrument 12, therebyallowing electrosurgical instrument 12 to be easily manipulated by asurgeon. Alternatively, the fluid source 14 can be directly connectedto, or incorporated into, the handle 20. For example, a pressurizedcanister of conductive fluid may be directly connected to the handle 20.Further, the fluid source 14 can comprise a syringe, a squeeze bulband/or some other fluid moving means, device or system.

[0080] In another embodiment, the fluid source 14 further includes asurgeon-controlled switch (not shown). For example, a switch may beincorporated in or on the fluid source 14 or any other location easilyand quickly accessed by a surgeon for regulation of conductive fluiddelivery. The switch may be, for example, a hand switch, a foot switch,or a voice-activated switch comprising voice-recognition technologies.

[0081] In yet another alternative embodiment, the fluid source 14includes a visual and/or audible signaling device (not shown) used toalert a surgeon to any change in the delivery of conductive fluid. Forexample, a beeping tone or flashing light can be used to alert thesurgeon that a change has occurred in the delivery of conductive fluid.

[0082] The power source 16 is of a type known in the art, and ispreferably a radio-frequency (RF) generator. The generator can bepowered by AC current, DC current or it can be battery powered either bya disposable or re-chargeable battery. The generator can incorporate acontroller (not shown) or any suitable processor to control power levelsdelivered to the electrosurgical instrument 12 based on informationsupplied to the generator/controller.

[0083] The above-described electrosurgical system 10, including theelectrosurgical instrument 12, is useful for a number of differenttissue ablation and cauterization procedures. For example, theelectrosurgical system 10 can be used to remove hemorrhoids or varicoseveins or stop esophageal bleeding to name but a few possible uses.Additionally, the electrosurgical system 10 is highly useful for thesurgical treatment of cardiac arrhythmia, and in particular treatment ofatrial fibrillation via ablation of atrial tissue. To this end, the Mazeprocedure, such as described in Cardiovascular Device Update, Vol. 1,No. 4, July 1995, pp. 2-3, the teachings of which are incorporatedherein by reference, is a well known technique, whereby lesion patternsare created along specified areas of the atria. The Maze III procedure,a modified version of the original Maze procedure, has been described inCardiac Surgery Operative Technique, Mosby Inc., 1997, pp. 410-419, theteachings of which are incorporated herein by reference. In an effort toreduce the complexity of the surgical Maze procedure, a modified Mazeprocedure was developed as described in The Surgical Treatment of AtrialFibrillation, Medtronic Inc., 2001, the teachings of which areincorporated herein by reference.

[0084]FIG. 7A depicts use of the electrosurgical system 10, and inparticular the electrosurgical instrument 12, performing a portion ofthe Maze procedure. In particular, FIG. 7A includes a representation ofa heart 70 with its left atrium 72 exposed. Prior to use, theelectrosurgical instrument 12 is provided to the surgeon (not shown)with the shaft 22 in the initial straight state (FIG. 1). The surgeonthen evaluates the constraints presented by the tissue target site 74and the desired lesion pattern to be formed. Following this evaluation,the surgeon determines an optimal shape of the shaft 22 most conduciveto achieving the desired ablation/lesion pattern. With this evaluationin mind, the surgeon then transitions or bends the shaft 22 from theinitial straight state to the bent state illustrated in FIG. 7A. Onceagain, the shaft 22 is configured to independently maintain thisselected shape. The shaft 22 can be bent by hand and/or by use ofbending jigs or tools.

[0085] Once the desired shape of the shaft 22 has been achieved, the tip44 is directed to the tissue target site 74. An indifferent electrode(18 in FIG. 1, but not shown in FIG. 7A) is placed in contact with thepatient. Conductive fluid from the fluid source 14 (FIG. 1) is deliveredto the tissue target site 74 via the internal lumen 50 (FIG. 3), thepassages 52 and/or the porous tip 44. Once sufficient fluid flow hasbeen established, the tip 44 is energized via the power source 16 (FIG.1). The tip 44, in turn, energizes the distributed fluid, therebycreating a virtual electrode that ablates contacted tissue. The surgeonthen slides or drags the tip 44 along the left atrium 70 tissue, therebycreating a desired lesion pattern 78, as best shown in FIG. 7B. In thisregard, the rigid coupling between the shaft 22 and the handle 20 allowsthe tip 44 to easily be slid along the atrial tissue via movement of thehandle 20. Once the desired lesion pattern 78 has been completed,energization of the tip 44 is discontinued, as well as delivery ofconductive fluid from the fluid source 14. If additional lesion patternsare required, the surgeon again evaluates the target tissue site, andre-forms the shaft 22 accordingly.

[0086] Notably, the shaft 22 need not necessarily be bent to perform atissue ablation procedure. Instead, the tip 44 can be drug across thetarget site tissue 74 with the shaft 22 in the initial straight state.In this regard, because the shaft 22 is straight and the handle 20(FIG. 1) is preferably circumferentially uniform, the electrosurgicalinstrument 12 does not have a discernable drag direction (as compared tothe shaft 22 being bent or curved, whereby the curve inherently definesa most appropriate drag direction).

[0087] In addition to the exemplary procedure described above, theelectrosurgical instrument 12 may be positioned and used, for example,through a thoracotomy, through a stemotomy, percutaneously,transveneously, arthroscopically, endoscopically, for example, through apercutaneous port, through a stab wound or puncture, through a smallincision, for example, in the chest, in the groin, in the abdomen, inthe neck or in the knee, or in combinations thereof. It is alsocontemplated that the electrosurgical instrument 12 may be used in otherways, for example, in open-chest surgery on a heart in which the sternumis split and the rib cage opened with a retractor.

[0088] The electrosurgical system 10, and in particular theelectrosurgical instrument 12, described above with respect to FIG. 1 isbut one acceptable configuration in accordance with the presentinvention. That is to say, the system 10 and/or the instrument 12 canassume other forms and/or include additional features while stillproviding an electrosurgical instrument having a shaft thatindependently maintains varying shapes associated with a straight stateand a bent state, and is indifferent to rotational orientation in thestraight state.

[0089] For example, the electrosurgical instrument 12 can include asurgeon-controlled switch. For example, a switch may be incorporated inor on the electrosurgical instrument 12 or any other location easily andquickly accessed by the surgeon for regulation of the electrosurgicalinstrument 12 by the surgeon. The switch may be, for example, a handswitch, a foot switch, or a voice-activated switch comprisingvoice-recognition technologies. One or more switches may be incorporatedinto the grip portion 24 of the electrosurgical instrument 12. Forexample, a switch may be used to control conductive fluid deliveryand/or power delivery. A switch incorporated into the grip portion 24may be a switch, such as a membrane switch, encompassing the entirecircumference of the electrosurgical instrument 12, thereby effectivelybeing indifferent to a rotational orientation when the surgeon graspsthe handle. That is to say, due to the cross-sectional shape of theswitch, the electrosurgical instrument 12 may be rotated to any positionrelative to a central axis A, and still be conveniently controlled bythe surgeon.

[0090] Alternatively, a hand switch connected to the electrosurgicalinstrument 12, but not incorporated into the electrosurgical instrument12, may be used. For example, a switch designed to be worn by a surgeon,for example on a surgeon's thumb, may be used to activate and/ordeactivate the electrosurgical instrument 12. A switch may beincorporated into a cuff or strap that is placed on or around the thumbor finger of a surgeon. Alternatively, a switch may be designed to fitcomfortably in a surgeon's palm.

[0091] One or more visual and/or audible signals used to alert a surgeonto the completion or resumption of ablation, conductive fluid deliveryand/or power delivery, for example, may be incorporated into theelectrosurgical instrument 12. For example, a beeping tone or flashinglight that increases in frequency as the ablation period ends or beginsmay be used. Alternatively or in addition, an indicator light otherwiselocated on the electrosurgical instrument can be inductively coupled tothe power source 16 and adapted such that when power is being deliveredto the electrosurgical instrument 12, the light is visible to thesurgeon or other users.

[0092] An alternative embodiment electrosurgical instrument 112 isprovided in FIGS. 8A and 8D. The electrosurgical instrument 112 ishighly similar to the electrosurgical instrument 12 (FIG. 1) previouslydescribed, and includes a handle 120, a shaft 122, a fluid supply tube126 and wiring 128. The shaft 122 is virtually identical to the shaft 22(FIG. 1) previously described, and forms a tip 124 having passages (notshown) fluidly connected to an internal lumen (not shown). Further, theshaft 122 is adapted to be bendable from a straight state (FIG. 8A) tomultiple bent states (one of which is illustrated in FIG. 8B), with theshaft 122 independently maintaining a shape associated with theparticular state. Similar to previous embodiments, the fluid supply tube126 fluidly connects the fluid source 14 (FIG. 1) to the shaft 122,whereas the wiring 128 electrically connects the power source 16(FIG. 1) to the shaft 122.

[0093] The handle 120 varies from the handle 20 (FIG. 1) previouslydescribed in that the handle 120 does not define a curved outer surface.Instead, the handle 120 is hexagonal in transverse cross-section. Thisalternative configuration is, however, indifferent to rotationalorientation when grasped by a user, thereby promoting the preferred easeof use feature previously described. Notably, the handle 120 canalternatively be formed to a variety of other symmetrical transversecross-sectional shapes (e.g., circular, octagonal, etc.).

[0094] In yet another alternative embodiment, the electrosurgical system10 (FIG. 1) further includes a controller (not shown) that can alsogather and process information from the electrosurgical instrument 12,120, fluid source 14 and/or one or more sensors or sensing elements suchas temperature sensors or probes. The information supplied to orgathered by the controller can be used to adjust, for example,conductive fluid delivery, power levels, and/or energization times. Forexample, a temperature sensor coupled to the controller can be locatedin the distal section 42 (FIG. 1) of the electrosurgical instrument 12.The temperature sensor can be a thermocouple element that measures thetemperature of the tip 44 rather than the temperature of the conductivefluid or the temperature of the tissue being ablated. Alternatively, thetemperature sensor can be a thermocouple element that measures thetemperature of the conductive fluid or a thermocouple element thatmeasures the temperature of the tissue being ablated. When the ablationsite is being irrigated with a conductive fluid, the temperature of thetissue may differ to some degree from the temperature of the conductivefluid or the temperature of the tip 44.

[0095] Heat, 1.0 kcal/g, is required to raise the temperature of water,present at the ablation site, by 1° C. However, due to the uniquechemical structure of the water molecule, additional heat is requiredfor water to change phase from the liquid phase to the gaseous phase. Ifthe temperature at the ablation site exceeds 100° C., water will changephase, boil and may result in an audible “steam pop” within the tissue.This pop may damage and even rupture the tissue. Therefore, it isdesirable to prevent the ablation site from getting to hot. In addition,to form a permanent ablation lesion the temperature of the tissue at theablation site must be elevated to approximately 50° C. or greater. Forthese reasons, it is desirable to use one or more temperature-sensingelements such as, for example, thermocouples, thermisters,temperature-sensing liquid crystals, temperature-sensing chemicals,thermal cameras, and/or infrared (IR) fiber optics, to monitor thetemperature of the ablation site during the ablation procedure.

[0096] With the above in mind, FIGS. 9A-9C depict a portion of analternative embodiment electrosurgical device 140, and in particular adistal section 142 thereof. The electrosurgical instrument 140 is highlysimilar to previous embodiments, and includes a shaft 144 terminating atan electrically conductive tip 146 having passages 148 formed thereinthat are fluidly connected to an internal lumen 150. Further, theelectrosurgical instrument 140 includes a temperature probe 160 formonitoring tissue temperature of the tissue being ablated. Thetemperature probe 160 is placed at the tip 146. A ring of insulationmaterial 162 may be used to electrically and thermally isolate thetemperature probe 160 from the electrically conductive tip 146. Thepreferred central placement of the temperature probe 160 at the tip 146allows the temperature probe 160 to directly contact a tissue surface ina number of orientations. The preferred insulating material 162 helps toprevent the thermal mass of the tip 146 and the RF energy frominterfering with temperature information otherwise provided by the probe160.

[0097] An alternative embodiment for monitoring temperature includes anIR optical fiber system. As shown in FIGS. 10A-10D, an alternativeembodiment electrosurgical instrument 190 may include an optical fiber192 for monitoring temperature based on IR. The optical fiber 192 can bepositioned adjacent a tip 194 otherwise defined by the instrument 190(FIGS. 10A and 10B) or within the tip 194 itself (FIGS. 10C and 10D).

[0098] The above-described temperature-sensing elements 160, 192 can beused to adjust, for example, conductive fluid delivery, power levels,and/or ablation times. Temperature-sensing elements can be coupled to avisual and/or audible signal used to alert a surgeon to a variety ofthermal conditions. For example, a beeping tone or flashing light thatincreases in frequency as temperature of the tissue, the conductivefluid and/or electrosurgical instrument is increased and/or astemperature exceeds a predetermined amount can be used.

[0099] Along these same lines, the above-mentioned controller canincorporate one or more switches to facilitate regulation of the variouscomponents of the electrosurgical system 10 (FIG. 1) by the surgeon. Oneexample of such a switch is a foot pedal. The switch can also be, forexample, a hand switch as described above, or a voice-activated switchcomprising voice-recognition technologies. The switch can beincorporated in or on one of the surgeon's instruments, such as surgicalsite retractor, e.g., a sternal or rib retractor, or the electrosurgicalinstrument 12 (FIG. 1), or any other location easily and quicklyaccessed by the surgeon. The controller can also include a display orother means of indicating the status of various components to thesurgeon, such as a numerical display, gauges, a monitor display or audiofeedback.

[0100] Finally, a visual and/or audible signal used to alert a surgeonto the completion or resumption of ablation, sensing, monitoring, and/ordelivery of conductive fluid can be incorporated into the controller.For example, a beeping tone or flashing light that increases infrequency as the ablation or electrocautery period ends or begins can beprovided.

[0101] In yet another alternative embodiment, the fluid source 14 can beslaved to the electrosurgical instrument 12, the power source 16 and/orone or more sensors (as previously described). For example, the fluidsource 14 can be designed to automatically stop or start the delivery ofconductive fluid during the delivery of RF energy. Conversely, thedelivery of RF energy may be slaved to the delivery of conductive fluid.That is the delivery of RF energy to the tip 44 would be coupled to thedelivery of conductive fluid to the tip 44. If the flow of conductivefluid to the tip 44 were stopped, the RF energy delivered to the tip 44would also automatically stop. For example, a switch responsive to thedelivery of conductive fluid to the tip 44 for controlling RF energydelivery to the tip 44 can be incorporated into the electrosurgicalinstrument 12. The switch can be located, for example, within the shaft22 or the handle 20 of electrosurgical instrument 12.

[0102] With the above in mind, FIG. 11 illustrates a portion of analternative embodiment electrosurgical instrument 200 including a shaft202 extending from a handle (not shown). The shaft 202 includes anelectrically conductive tip 204 and a malleable, non-conductive tube 206rigidly connecting the tip 204 to the handle. An electrically conductingswitch piston 208 is located within the non-conductive tube 206. Theconducting switch piston 208 is electrically coupled to the power source16 (FIG. 1). The conducting switch piston 208 is movably held in anon-contacting position relative to the tip 204 by a spring or otherelastic means (not shown). As conductive fluid is delivered, a pressuredevelops behind an orifice 210 of the conducting switch piston 208. Thesize and shape of the orifice 210 is selected based on expected fluiddelivery rates and pressures. When the necessary pressure or force toover come the spring retaining pressure or force is reached, theconducting switch 208 travels distally towards the tip 204, therebymaking an electrical contact with the tip 204. Other means can be usedto slave the delivery of power to the tip 204 of the electrosurgicalinstrument 200 to the delivery of conductive fluid to the tip 204 of theelectrosurgical instrument 200. For example, the controller canincorporate one or more switches to facilitate the regulation of RFenergy based on the delivery of conductive fluid.

[0103] The incision patterns of a Maze III procedure are described inthe book ‘Cardiac Surgery Operative Technique’ by Donald B. Doty, M. D.at pages 410-419, incorporated herein by reference in its entirety, andhereafter referred to as the “Doty Reference.” The left atrial isthmuslesion 558 (see FIG. 12) extends from a pulmonary vein isolation lesion546, inferior of the pulmonary veins, crosses over the coronary sinusand ends at the mitral valve annulus 560. The lesion 558 corresponds tothe incision illustrated as step 5 as described in the Doty reference.The lesion 558 may be created via an epicardial or endocardial approach.The lesion may also be created via a coronary sinus approach comprisingthe advancement of electrode tip 44 of electrosurgical instrument 12into the coronary sinus 570. In particular, FIG. 12 is a schematicdrawing illustrating the right and left atria, 500, 502, respectively,as viewed from a lower aspect, including tricuspid valve 516, orifice ofcoronary sinus 570, and mitral valve 514 and as viewed from a moresuperior aspect, including the bases of the pulmonary veins 512 and thebases of the superior vena cava and inferior vena cava, 508, 510,respectively, which enter the right atrium 500. The right and leftatrial appendages are also illustrated schematically at 505 and 550,respectively. FIG. 13 is a schematic drawing illustrating the lesion 558crossing over the coronary sinus 570 and the circumflex artery 580 asviewed from a posterior view of the heart 70.

[0104] Prior to the ablation procedure, the surgeon evaluates theconstraints presented for advancing electrode tip 44 into the coronarysinus 570 from within the right atrium 500. Following this evaluation,the surgeon determines an optimal shape of the shaft 22 most conduciveto achieving the desired ablation lesion from within the coronary sinus570. With this evaluation in mind, the surgeon then transitions or bendsthe shaft 22 into a desired state. Once again, the shaft 22 isconfigured to independently maintain the selected shape.

[0105] Once the desired shape of the shaft 22 has been achieved, the tip44 is advanced into the right atrium 500 and into the coronary sinus570. Ablating tip 44 may be advanced into the right atrium 500 throughan incision, i.e., an atriotomy (not shown). If the heart is beating,i.e., the heart is not on cardiopulmonary bypass, a purse-string suturemay be used to minimize blood loss through the incision and around thedevice. Once inside the right atrium 500, tip 44 is advanced into thecoronary sinus 570 until tip 44 reaches the desired location within thecoronary sinus for creation of the ablation lesion 558. Proper ablativetip placement can be confirmed by palpitation of the coronary sinus, forexample, in an open-chest procedure. For procedures wherein the coronarysinus cannot be palpitated, electrosurgical instrument 12 may includeone or more additional features. For example, electrosurgical instrument12 may include a pressure monitoring sensor or port, thereby allowingone to monitor pressure during placement and use of the device.Pressures of the right atrium and the coronary sinus may be used toconfirm proper placement of the ablative tip 44 in the coronary sinus.Alternatively, an echo enhancing feature or material may be added toelectrosurgical instrument 12 thereby allowing the proper placement ofthe tip 44 into the coronary sinus to be confirmed via transesophagealechocardiography (TEE). Alternatively, electrosurgical instrument 12 mayinclude one or more light sources for lighting tip 44. An endoscopecould then be used to visually confirm proper placement of tip 44 in thecoronary sinus since the light emanating from the tip would shinethrough the thin tissue wall of the coronary sinus. Once tip 44 isadvanced into the coronary sinus at the proper depth or distance,conductive fluid from the fluid source 14 (FIG. 1) is delivered to theablation area via the internal lumen 50 (FIG. 3), the passages 52 and/orthe porous tip 44. Once sufficient fluid flow has been established, tip44 is energized via the power source 16 (FIG. 1). The tip 44, in turn,energizes the distributed fluid, thereby creating a virtual electrodethat ablates contacted tissue within the coronary sinus. Once the lesion558 has been completed, energization of the tip 44 is discontinued, aswell as delivery of conductive fluid from the fluid source 14. Ifadditional lesions are required, the surgeon again evaluates the targettissue site, and re-forms the shaft 22 accordingly.

[0106] It is contemplated that the ablation lesion 558 may be createdvia placement of one or more ablative elements within the coronarysinus. In addition, it is contemplated that one or more ablativeenergies may be used with one or more ablative elements to createablation lesion 558, for example, radiofrequency energy, ultrasoundenergy, laser energy, microwave energy, and/or combinations thereof, maybe used. Alternatively, one or more cryo ablation elements could beplaced within the coronary sinus to form lesion 558.

[0107] In yet another embodiment, and with general reference to FIG. 1,the electrosurgical instrument 12, the fluid source 14 and/or the powersource 16 can be slaved to a robotic system or a robotic system may beslaved to the electrosurgical instrument 12, the fluid source 14 and/orthe power source 16.

[0108] The electrosurgical system, and in particular the electrosurgicalinstrument, of the present invention provides a marked improvement overprevious designs. The handle and shaft are configured to be indifferentto rotational orientation when initially presented to a surgeon.Subsequently, the surgeon can conveniently shape or bend the shaft so asto provide a shape most conducive to forming the lesion pattern requiredby the particular surgical procedure. In this regard, the shaftindependently maintains the selected shape throughout the particularelectrosurgical procedure. Subsequently, the shaft can be re-shaped backto a straight configuration, or to any other desired curvature.

[0109] One embodiment of a mapping system 310 in accordance with thepresent invention is shown in FIG. 14. The system 310 is comprised of amapping instrument 312, a diagnostic device 316 and an indifferentelectrode 318. The various components are described in greater detailbelow. In general terms, the diagnostic device 316 is electricallyconnected to the mapping instrument 312 and to the indifferent orgrounding electrode 318. In one embodiment, the diagnostic device 316may be the Medtronic Programmer/Analyzer model 2090/2290 which has thecapability of pacing and sensing.

[0110] The mapping instrument 312 includes a handle 320 and a shaft 322.As described in greater detail below, the shaft 322 is rigidly coupledto the handle 320, and is transitionable from a straight state (asillustrated in FIGS. 14 and 15A) to a bent state (for example as shownin FIGS. 15B and 15C). In this regard, the shaft 322 independentlymaintains the shape associated with the particular state (i.e., straightor bent).

[0111] The handle 320 is preferably made of a sterilizable, rigid, andnon-conductive material, such as a polymer or ceramic. Suitable polymersinclude rigid plastics, rubbers, acrylics, nylons, polystyrenes,polyvinylchlorides, polycarbonates, polyurethanes, polyethylenes,polypropylenes, polyamides, polyethers, polyesters, polyolefins,polyacrylates, polyisoprenes, fluoropolymers, combinations thereof orthe like. Further, the handle 20 is ergonomically designed tocomfortably rest within a surgeon's hand (not shown). To this end, thehandle 320 may include a grip portion 324 that is circular in crosssection. This configuration facilitates grasping of the handle 320, andthus of the mapping instrument 312, at any position along the gripportion 324 regardless of an overall rotational orientation of themapping instrument 312. That is to say, due to the circular,cross-sectional shape of the grip portion 324, the mapping instrument312 can be rotated to any position relative to a central axis A, andstill be conveniently grasped by the surgeon. In one embodiment, thegrip portion 324 defines a gradual, distally increasing diameter thatprovides an orientation feature to help a surgeon identify where alongthe length of the mapping instrument 312 he or she is grasping. Forexample, if the surgeon grasps the mapping instrument 312 out of hisvisual sight during a medical procedure, the surgeon may identify basedon the grip portion's 324 diameter where along the instrument he hasgrasped. Finally, the grip portion 324 may be formed of a low durometerpolymer. Suitable polymers include low durometer plastics, rubbers,silicones, acrylics, nylons, polystyrenes, polyvinylchlorides,polycarbonates, polyurethanes, polyethylenes, polypropylenes,polyamides, polyethers, polyesters, polyolefins, polyacrylates,polyisoprenes, fluoropolymers, combinations thereof or the like. Thegrip portion 324 alternatively may be a sponge-like or foam-likematerial, such as an open-cell material or a closed-cell material.

[0112] Regardless of exact configuration, the handle 320 may form orencompass one or more central lumens (not shown). The lumen(s) canprovide a pathway for a line or wiring 328 from the diagnostic device316 to the shaft 322. In this regard, FIG. 16 illustrates the mappinginstrument 312 with the handle 320 removed. The line 328 from thediagnostic device 316 (FIG. 14) is shown as extending to, and beingelectrically connected with, the shaft 322.

[0113] Returning to FIG. 14, the shaft 322 is an elongated, relativelyrigid component defining a proximal section 340 and a distal section342. The distal section 342 terminates in an electrically conductive tip344. As described in greater detail below, the tip 344 may be rounded,defining a uniform radius of curvature. In one embodiment, the tip 344may be shaped like a round ball. The tip 344 may be textured. With thetip being in a rounded configuration, the tip 344 is, similar to thehandle 320, indifferent to rotational orientation of the mapping device312. That is to say, regardless of how a surgeon (not shown) grasps thehandle 320 (i.e., the rotational position of the handle 320 relative tothe central axis A), a profile of the tip 344 in all directions (e.g.,in front of the surgeon's thumb position, behind the surgeon's thumbposition, etc.) is always the same so that the tip 344 is readilymaneuvered along tissue (not shown) in any direction. To this end, therounded shape can facilitate a sliding movement of the tip 344 along thetissue.

[0114] A preferred feature of the shaft 322 is a malleable or shapeablecharacteristic. In particular, and with additional reference to FIGS.15A-15C, the shaft 322 is configured to be transitionable from aninitial straight state (FIG. 15A) to a bent or curved state (FIGS. 15Band 15C). In this regard, the mapping instrument 312, and in particularthe shaft 322, is initially presented to a surgeon (not shown) in thestraight state of FIG. 15A, whereby the shaft 322 assumes a straightshape defining the central axis A. In the straight state, the shaft 322is indifferent to rotational orientation, such that the mappinginstrument 312 can be grasped at any rotational position and the tip 344will be located at an identical position. Further, as previouslydescribed, a profile of the tip 344 is also uniform or identical at anyrotational position of the mapping instrument 312. Subsequently,depending upon the constraints of a particular mapping procedure, theshaft 322 can be bent relative to the central axis A. Two examples of anapplicable bent state or shape are provided in FIGS. 15B and 15C. In apreferred embodiment, the shaft 322 can be bent at any point along alength thereof, and can be formed to include multiple bends or curves.Regardless, the shaft 322 is configured to independently maintain theshape associated with the selected bent shape. That is to say, the shaft322 does not require additional components (e.g., pull wires, etc.) tomaintain the selected bent shape. Further, the shaft 322 is constructedsuch that a user can readily re-shape the shaft 322 back to the straightstate of FIG. 15A and/or other desired bent configurations. Notably, theshaft 322 is configured to relatively rigidly maintain the selectedshape such that when a force is imparted onto the shaft 322 as the tip344 contacts tissue, the shaft 322 will not overtly deflect from theselected shape.

[0115] In one preferred embodiment, the above-described characteristicsof the shaft 322 are achieved by forming the shaft 322 to include anelongated electrode body 360 and an electrical insulator covering 362 asshown in FIGS. 14 and 17. The electrode body 360 defines the proximalsection 340 and the distal section 342 of the shaft 322. To this end,the proximal section 340 of the electrode body 360 is rigidly coupled tothe handle 320. The insulator 362 covers a substantial portion of theelectrode body 360, preferably leaving the distal section 342 exposed.In particular, the insulator 362 is positioned to encompass an entiretyof the electrode body 360 distal the handle 320 and proximal the distalsection 342 (and in particular, proximal the tip 344).

[0116] In one preferred embodiment, the electrode body 360 is formed ofan electrically conductive, malleable material, preferably stainlesssteel, however other materials such as, for example, nitinol can beused. The insulator 362 is formed of one or more electricallynon-conductive materials, e.g., a nonconductive fluoropolymer, andserves to electrically insulate the encompassed portion of the electrodebody 360. Multiple layers of electrically non-conductive materials canhelp prevent the likelihood of forming an electrical short along thelength of the electrode body 360 due to a mechanical failure of one ofthe non-conductive materials. In this regard, the insulator 362 ispreferably comprised of two materials having considerably differentmechanical properties, e.g., a silicone and a fluoropolymer. In oneembodiment, a silicone tubing material is overlaid with a heat shrinkfluoropolymer tubing material. Alternatively, the insulator 362 may beone or more non-conductive coatings applied over a portion of theelectrode body 360. In addition to being non-conductive, the insulator362 is preferably flexible and conforms to the electrode body 360 suchthat the insulator 362 does not impede desired shaping and re-shaping ofthe electrode body 360 as previously described.

[0117] It will be understood that the preferred construction of theshaft 322 to include the elongated electrode body 360 and the insulator362 is but one available configuration. Alternatively, the shaft 322 canbe constructed of an electrode material forming the tip 344, and a rigidor malleable, non-conductive rod or tube rigidly connecting the tip 344to the handle 320. The non-conductive rod or tube can include one ormore metal conductors, such as straight wire and/or windings forelectrically connecting the tip 344 to the diagnostic device 316. Thetip 344 may be coated with one or more coatings. Another alternativeembodiment includes construction of the shaft 322 to include one or moremetal conductors, such as straight wire and/or windings inside a rigidor malleable non-conductive polymer tube. The insulator 362 may cover aportion of the wire or windings.

[0118] With respect to the above-described alternative embodiments,connection between the elongated rod or tube and the separate tip 344can be accomplished in a variety of manners. Once again, the elongatedrod or tube can comprise a conductive or non-conductive material(s),such as metal(s) or plastic(s). The elongated rod or tube can beconnected to the tip 344 via a variety of coupling techniques,including, for example, welding, laser welding, spin welding, crimping,gluing, soldering and press fitting. Alternatively, the distal end ofthe elongated rod or tube and the tip 344 can be configured tothreadably engage one another and/or mechanical engagement member(s)(e.g., pins, screws, rivets, etc.) can be employed. In anotherembodiment, the elongated rod or tube is rigidly coupled to the tip 344.In yet another embodiment, the tip 344 can be moveably coupled to theelongated rod or tube, whereby the tip 344 can be moved and/or lockedrelative to the elongated rod or tube. For example, the tip 344 can becoupled to the elongated rod or tube via one or more joints or hinges.The joints or hinges can be ball joints and/or joints that include apin. To this end, a pin-type joint can be configured to allow the tip344 to swivel relative to the elongated rod or tube. Further, thejoint(s) can be configured to move and lock into position. In addition,one or more actuators (e.g., knobs, buttons, levers, slides, etc.) canbe located on, for example, the handle 320 (FIG. 1) for actuating thejoint(s). With the above in mind, FIG. 18 illustrates a portion of analternative embodiment shaft 322′ including a tip 344′ moveably coupledto an elongated rod or tube 363 by a pin 364.

[0119] Returning to FIG. 14, the mapping instrument 312 preferablyincludes a coupling member 365 for rigidly coupling the shaft 322 to thehandle 320. The coupling member 365 can comprise one or more polymers,plastics, and/or rubbers. For example, the coupling member 365 cancomprise one or more silicones, acrylics, nylons, polystyrenes,polyvinylchlorides, polycarbonates, polyurethanes, polyethylenes,polypropylenes, polyamides, polyethers, polyesters, polyolefins,polyacrylates, polyisoprenes, fluoropolymers, combinations thereof orthe like.

[0120]FIG. 19A depicts use of the mapping system 310, and in particularthe mapping instrument 312, performing an assessment of transmurality ofone or more ablation lesions 78 created by an ablation tool, for exampleelectrosurgical instrument 12. Transmurality is achieved when the fullthickness of the target tissue is ablated. In particular, FIG. 19Aincludes a representation of a heart 70 with its left atrium 72 exposed.Prior to use, the mapping instrument 312 is provided to the surgeon (notshown) with the shaft 322 in the initial straight state (FIG. 14). Thesurgeon then evaluates the constraints presented by the tissue targetsite 74 and the lesion pattern 78 formed earlier by an ablationprocedure. Following this evaluation, the surgeon determines an optimalshape of the shaft 322 most conducive to achieving the desiredassessment. With this evaluation in mind, the surgeon then transitionsor bends the shaft 322 from the initial straight state to the bent stateillustrated in FIG. 19A. Once again, the shaft 322 is configured toindependently maintain this selected shape. The shaft 322 can be bent byhand and/or by use of bending jigs or tools.

[0121] Once the desired shape of the shaft 322 has been achieved, thetip 344 is directed to the tissue target site 74. A grounding electrode(318 in FIG. 14, but not shown in FIG. 19A) is placed in contact withthe patient. The grounding electrode may comprise a needle electrode anda cable for connection to the diagnostic device 316. Alternatively, agrounding wire may be coupled to diagnostic device 316 and a metalretractor coupled to the patient. For example, a metal sternal retractorused to spread a patient's ribs may be used as a grounding electrode.

[0122] If additional lesions are to be assessed, the surgeon againevaluates the target tissue site, and re-forms the shaft 322accordingly. Notably, the shaft 322 need not necessarily be bent toperform a tissue mapping/pacing procedure. Instead, the tip 344 cancontact the target site tissue 74 with the shaft 322 in the initialstraight state. In this regard, because the shaft 322 is straight andthe handle 320 (FIG. 14) is preferably circumferentially uniform, themapping instrument 312 does not have a discernable use direction (ascompared to the shaft 322 being bent or curved, whereby the curveinherently defines a most appropriate use direction).

[0123] In addition to the one exemplary procedure described above, themapping instrument 312 may be positioned and used, for example, througha thoracotomy, through a sternotomy, percutaneously, transveneously,endoscopically, for example, through a percutaneous port, through a stabwound or puncture, through a small incision, for example, in the chestor in the abdomen, or in combinations thereof. It is also contemplatedthat the mapping instrument 312 may be used in other ways, for example,in open-chest surgery on a heart in which the sternum is split and therib cage opened with a retractor.

[0124] The mapping system 310, and in particular the mapping instrument312, described above with respect to FIG. 14 is but one acceptableconfiguration in accordance with the present invention. That is to say,the system 310 and/or the instrument 312 can assume other forms and/orinclude additional features while still providing a mapping instrumenthaving a shaft that independently maintains varying shapes associatedwith a straight state and a bent state, and is indifferent to rotationalorientation in the straight state.

[0125] For example, the mapping instrument 312 can include one or moresurgeon-controlled switches. For example, a switch may be incorporatedin or on the mapping instrument 312 or any other location easily andquickly accessed by the surgeon for regulation of the mapping instrument312 by the surgeon. The switch may be, for example, a hand switch, afoot switch, or a voice-activated switch comprising voice-recognitiontechnologies. One or more switches may be incorporated into the gripportion 324 of the mapping instrument 312. A switch incorporated intothe grip portion 324 may be a switch, such as a membrane switch,encompassing the entire circumference of the mapping instrument 312,thereby effectively being indifferent to a rotational orientation whenthe surgeon grasps the handle. That is to say, due to thecross-sectional shape of the switch, the mapping instrument 312 may berotated to any position relative to a central axis A, and still beconveniently controlled by the surgeon.

[0126] Alternatively, a hand switch connected to the mapping instrument312, but not incorporated into the mapping instrument 312, may be used.For example, a switch designed to be worn by a surgeon, for example on asurgeon's thumb, may be used to activate and/or deactivate the mappinginstrument 312. A switch may be incorporated into a cuff or strap thatis placed on or around the thumb or finger of a surgeon. Alternatively,a switch may be designed to fit comfortably in a surgeon's palm.

[0127] One or more visual and/or audible signals used to alert a surgeonto the completion or resumption of a procedure, for example, may beincorporated into the mapping instrument 312. For example, a beepingtone or flashing light that increases in frequency as the mapping/pacingperiod ends or begins may be used. Alternatively or in addition, anindicator light otherwise located on the mapping instrument 312 can beinductively coupled to the diagnostic device 316 and adapted such thatwhen power is being delivered to the mapping instrument 312, the lightis visible to the surgeon or other users.

[0128] An alternative embodiment, mapping instrument 412 is provided inFIGS. 20A and 20D. The mapping instrument 412 is highly similar to themapping instrument 312 (FIG. 14) previously described, and includes ahandle 420, a shaft 422 and wiring 428. The shaft 422 is virtuallyidentical to the shaft 322 (FIG. 14) previously described, and forms atip 444. The shaft 422 is adapted to be bendable from a straight state(FIG. 20A) to multiple bent states (one of which is illustrated in FIG.20B), with the shaft 422 independently maintaining a shape associatedwith the particular state. Similar to previous embodiments, the wiring428 electrically couples the diagnostic device 316 (FIG. 14) to theshaft 422.

[0129] The handle 420 varies from the handle 320 (FIG. 14) previouslydescribed in that the handle 420 does not define a curved outer surface.Instead, the handle 420 is hexagonal in transverse cross-section. Thisalternative configuration is, however, indifferent to rotationalorientation when grasped by a user, thereby promoting the preferred easeof use feature previously described. Notably, the handle 420 canalternatively be formed to a variety of other symmetrical transversecross-sectional shapes (e.g., octagonal, etc.).

[0130] In yet another alternative embodiment, the mapping system 310(FIG. 14) further includes a controller (not shown) that can also gatherand process information from the mapping instrument 312 and/or one ormore sensors or sensing elements such as temperature sensors or probes.For example, a temperature sensor coupled to the controller can belocated in the distal section 342 (FIG. 14) of the mapping instrument312. The temperature sensor may be a thermocouple element that measurestissue temperature. Alternatively, the temperature sensor may be, forexample, one or more thermisters, temperature-sensing liquid crystals,temperature-sensing chemicals, thermal cameras, and/or infrared (IR)fiber optics.

[0131] With the above in mind, FIGS. 21A-21C depict a portion of analternative embodiment mapping device 640, and in particular a distalsection 642 thereof. The mapping instrument 640 is highly similar toprevious embodiments, and includes a shaft (not shown) terminating at anelectrically conductive tip 644. Further, the mapping instrument 640includes one or more sensors 660, for example, a temperature probe formonitoring tissue temperature. The sensor 660 may be placed at the tip644. A ring of insulation material 663 may be used to electrically andthermally isolate sensor 660 from the electrically conductive tip 644.The preferred central placement of the sensor 660 at the tip 644 allowsthe sensor 660 to directly contact a tissue surface in a number oforientations. An alternative embodiment sensor 660 may include an IRoptical fiber system, for example, to monitor temperature based on IR.The sensor 660 may be positioned adjacent tip 644 (not shown) or withintip 644 (FIGS. 21A-21C).

[0132] Sensing elements 660 can be coupled to visual and/or audiblesignals used to alert a surgeon to a variety of procedural conditions.For example, a beeping tone or flashing light that increases infrequency as temperature of the tissue exceeds a predetermined amountcan be used.

[0133] In one embodiment, diagnostic device 316 can incorporate one ormore switches to facilitate regulation of various components of mappingsystem 310 (FIG. 14) by the surgeon. One example of such a switch is afoot pedal. The switch can also be, for example, a hand switch asdescribed above, or a voice-activated switch comprisingvoice-recognition technologies. The switch can be incorporated in or onone of the surgeon's instruments, such as surgical site retractor, e.g.,a sternal or rib retractor, or the mapping instrument 312 (FIG. 14), orany other location easily and quickly accessed by the surgeon. Thediagnostic device 316 can also include a display or other means ofindicating the status of various components to the surgeon, such as anumerical display, gauges, a monitor display or audio feedback.

[0134] Finally, a visual and/or audible signal used to alert a surgeonto the completion or resumption of sensing, monitoring, pacing and/ormapping can be incorporated into the controller. For example, a beepingtone or flashing light that increases in frequency as the pacing periodends or begins can be provided.

[0135] In yet another embodiment, and with general reference to FIG. 14,the mapping instrument 312 and/or the diagnostic device 316 can beslaved to a robotic system or a robotic system may be slaved to themapping instrument 312 and/or the diagnostic device 316.

[0136] The handle and shaft of the mapping instrument of the presentinvention are configured to be indifferent to rotational orientationwhen initially presented to a surgeon. Subsequently, the surgeon canconveniently shape or bend the shaft so as to provide a shape mostconducive to assessing the lesion pattern required by the particularsurgical procedure. In this regard, the shaft independently maintainsthe selected shape throughout the particular mapping/pacing procedure.Subsequently, the shaft can be re-shaped back to a straightconfiguration, or to any other desired curvature.

[0137] In one embodiment, mapping instrument 312 may be used to pace theheart. For example, mapping instrument 312 may be connected to anexternal temporary pacemaker, e.g., the Medtronic External TemporaryPacemaker model 5388 or the Medtronic 2090/2290 Programmer/Analyzer.Mapping instrument 312 may be used to temporarily pace atrial tissue ofthe heart and/or ventricular tissue of the heart. For pacing the heart,tip 344 of mapping instrument 312 is put into contact with tissue to bepaced. For example, in one embodiment, a textured ball tip electrode 344is placed into contact with atrial tissue (FIGS. 19A and 19B).

[0138] In one embodiment, a pacing threshold for the mapping instrument312 for pacing atrial tissue is <10 mA@ 0.5 ms using the Medtronic 5388pacemaker. Medtronic's 5388 pacemaker has a maximum output of 20 mA.Ablation lesion testing may be performed by finding the pacing thresholdoutside the isolated tissue area 74 and then placing the device insidethe isolated tissue area 74, as shown in FIGS. 19A and 19B, with 2× thepacing threshold of the non-isolated area. A pacing threshold of 10 mAor less allows the mapping instrument 312 to be used for typical lesiontesting after cardiac ablation of atrial tissue 78. Since the Medtronic5388 device is a current controlled device, pacing threshold for the5388 temporary pacemaker is the minimum current at which the temporarypacemaker continuously controls pacing of the heart.

[0139] The pacing threshold for the mapping instrument 312 for pacingventricle tissue is <5V@ 0.5 ms using Medtronic's 2090/2290Programmer/Analyzer and the resistance at 5V preferably is >500 Ω(5V/500Ω=10 mA). Pacing threshold for the Programmer/Analyzer is thelowest voltage at which continuous capture of the heart occurs. Mappinginstrument 312 is used in a unipolar mode (measuring between the tip 344and a grounding electrode 318, for example a grounding needle placed,for example, in the extrathoracic tissue). Pacing resistance can bemeasured at 5V while using the Programmer/Analyzer to measure pacingthresholds.

[0140] In one embodiment, the mapping instrument 312 can be used in leftsided epicardial lead placement procedures. During these procedures,epicardial mapping is useful in identifying the optimal site forepicardial lead placement on the left ventricle. In one embodiment, themapping instrument 312 is used to pace one or more ventricles and thesynchronicity of left ventricular contraction is evaluated, for example,with TEE. Alternatively, tissue Doppler ultrasound may be used tomeasure contraction patterns and to locate the site where biventricularpacing could result in the most effective contraction of the leftventricle. While Doppler ultrasound may be may be more effective thanTEE, it is not commonly available and may require the patient's chest tobe closed in order to provide useful data.

[0141] Another approach entails identifying the site of latest leftventricular electrical activity following a paced right ventricularbeat. This electrical site may correlate with the site of latestmechanical activity. Pacing at the site of latest activation can createtwo contraction wavefronts from electrically opposite sides of the heartwhile accommodating any unusual conduction pathways. Theoretically, thiswill create collision of the right and left ventricular wavefrontsequidistant from the electrodes on both sides of the ventricle therebyminimizing dysynchrony. The hypothesis for this activation sequence wasoriginally described more than 20 years ago. FIG. 22 illustratesactivation patterns 390 and cell-to-cell conduction from rightventricular pacing by an electrode 395 placed in the right ventricle.

[0142] The approach of identifying the site of latest left ventricularelectrical activity determines the time between a paced event in theright ventricle and the corresponding sensed event in the leftventricle. As the heart is paced in the right ventricle, the electrodetip 344 of mapping instrument 312 is placed into contact of epicardialtissue of the left ventricle and the time at which a depolarization waveis sensed over the left ventricle is noted.

[0143] This timeframe is called the “paced depolarization interval”(PDI). Starting at a posterior lateral position, approximately six sitesshould be measured, see FIG. 23. The longest time interval or maximumPDI is the point that is electrically farthest from the rightventricular electrode and is generally the site for optimal leadplacement.

[0144] Paced depolarization intervals will vary among patients. PDIvalues of normal hearts are usually 100 ms or less, but patients whohave congestive heart failure and larger hearts typically have valuesbetween 150 ms and 200 ms. In general, the larger the heart, the largerthe PDI. In addition, PDIs below 150 ms tend to indicate the leadlocation is not optimal.

[0145] When measuring paced depolarization intervals, it is veryimportant to use a paced beat rather than an intrinsic beat. A CRTsystem will pace both ventricles and the lead placement site should bechosen in accordance with the way the CRT system functions. Pacing ofthe right ventricle can be accomplished using either an implantedpacemaker or a programmer/analyzer, for example, the Medtronic 2090/2290Programmer/Analyzer.

[0146] If the patient already has an implanted pacemaker, it is notnecessary to remove it or externalize the right ventricular lead priorto mapping for left ventricular lead placement. The pacemaker should beprogrammed to pace the right ventricle continuously in the unipolarmode. A 5V pacing pulse may be used to help visualization of the pacingspike on the mapping electrode signal. Mapping instrument 312 should beconnected to the programmer or other device to display electrograms(EGMs), which should either be frozen electronically in the programmeror printed on paper for manual measurement. From the EGM, the pacingspike should be seen, as should the depolarization wavefront that passesunder the left ventricular mapping electrode. The time between thepacing spike and the depolarization wave on the EGM signal is the PDI.Maximizing the PDI may optimize cardiac resynchronization.

[0147] A Programmer/Analyzer, for example, the Medtronic 2090/2290Programmer/Analyzer, may be used to measure the maximum PDI. If a rightventricular lead is not accessible, the mapping electrode can beconnected to either the atrial or ventricular channel of the analyzer.The pacing spike and the depolarization wavefront should both be visibleon the data strip, see FIG. 24. During this measurement, the rightventricular lead should be pacing the heart with the implanted pacemakerin the unipolar mode. The time can then be measured between the pacingspike and the left ventricular deflection.

[0148] If the right ventricular lead is accessible, both leads can beconnected to the analyzer. The right ventricular lead is connected tothe ventricular channel and the mapping instrument 312 is connected tothe atrial channel. The analyzer can then pace the right ventricularlead, sense the left ventricular mapping electrode, and display the timebetween the paced and sensed events on the screen. In this case, theright ventricular (RV) and left ventricular (LV) EGMs shown in FIG. 25will both be visible. The strips can be frozen electronically in theanalyzer and the maximum PDI measured with calipers, or they can beprinted on paper for manual measurement.

[0149] In another embodiment, the electrosurgical instrument 12 includesa mode switch (not shown). For example, a surgeon-controlled mode switchmay be incorporated in or on the electrosurgical instrument 12 or anyother location easily and quickly accessed by a surgeon for switchingbetween an ablation mode, a mapping mode and/or a pacing mode. Theswitch may be, for example, a hand switch, a foot switch, or avoice-activated switch comprising voice-recognition technologies. A modeswitch would allow the electrosurgical instrument 12 to be used as bothan ablation tool and a mapping/pacing tool. For example, an energysource may be electrically connected to electrosurgical instrument 12,wherein the energy source comprises ablation energy for creating tissuelesions and stimulation energy for pacing the heart. A switch coupled tothe energy source may be configured to control delivery of ablationenergy and stimulation energy from the energy source to electrosurgicalinstrument 12. The delivery of ablation energy to electrosurgicalinstrument 12 may be stopped when the delivery of stimulation energy toelectrosurgical instrument 12 is started and the delivery of stimulationenergy to electrosurgical instrument 12 may be stopped when the deliveryof ablation energy to electrosurgical instrument 12 is started. Theswitch may also be coupled to a source of conductive fluid. In thiscase, the switch may be configured to control delivery of fluid from asource of conductive fluid to the internal lumen of the instrument. Forexample, the delivery of fluid to the internal lumen of the instrumentmay be stopped when the delivery of ablation energy to the tip of theinstrument is stopped and the delivery of fluid to the internal lumen ofthe instrument may be started when the delivery of ablation energy tothe tip of the instrument is started.

[0150] In yet another alternative embodiment, the electrosurgicalinstrument 12 includes a visual and/or audible signaling device (notshown) used to alert a surgeon to any change in the mode of the device.For example, a beeping tone or flashing light can be used to alert thesurgeon that the electrosurgical instrument 12 is in an ablation mode orhas changed from a mapping/pacing mode to an ablation mode. For example,one or more indicator lights located on the instrument can indicate thedelivery of ablation energy and/or stimulation energy for pacing hearttissue.

[0151] Although the invention has been described above in connectionwith particular embodiments and examples, it will be appreciated bythose skilled in the art that the invention is not necessarily solimited, and that numerous other embodiments, examples, uses,modifications and departures from the embodiments, examples and uses areintended to be encompassed by the claims attached hereto. The entiredisclosure of each patent and publication cited herein is incorporatedby reference, as if each such patent or publication were individuallyincorporated by reference herein.

What is claimed is:
 1. A system for pacing the heart comprising: aninstrument including: an elongated shaft defining a proximal section anda distal section, wherein the distal section forms an electricallyconductive rounded tip, and further wherein the shaft is adapted to betransitionable from a straight state to a first bent state, the shaftindependently maintaining distinct shapes in the straight state and thefirst bent state, and a non-conductive handle rigidly coupled to theproximal section of the shaft; wherein an exterior of the shaft distalthe handle and proximal the distal section is electricallynon-conductive; a grounding electrode; and an energy source electricallyconnected to the tip and the grounding electrode, wherein the energysource comprises stimulation energy for pacing the heart.
 2. The systemof claim 1, wherein the tip of the instrument defines a uniform radiusof curvature.
 3. The system of claim 1, wherein in the straight state,the shaft of the instrument defines a linear axis, and further whereinin the first bent state, a portion of the shaft is deflected relative tothe linear axis.
 4. The system of claim 3, wherein the shaft of theinstrument is adapted to be transitionable to, and independentlymaintain a shape in, any direction relative to the linear axis.
 5. Thesystem of claim 1, wherein the shaft of the instrument is capable ofbeing bent at a multiplicity of points along a length thereof.
 6. Thesystem of claim 1, wherein the shaft of the instrument is adapted to betransitionable to, and independently maintain a shape of, a second bentstate different from the first bent state.
 7. The system of claim 1,wherein the instrument is adapted for stimulating cardiac tissue througha chest of a patient.
 8. The system of claim 7, wherein the cardiactissue is atrial tissue.
 9. The system of claim 7, wherein the cardiactissue is ventricular tissue.
 10. The system of claim 7, wherein theinstrument is adapted for stimulating cardiac tissue endocardiallythrough a chest of a patient.
 11. The system of claim 7, wherein theinstrument is adapted for stimulating cardiac tissue epicardiallythrough a chest of a patient.
 12. The system of claim 1, wherein theshaft of the instrument includes: an elongated electrode body formingthe proximal section and the distal section, the electrode body beingdirectly coupled to the handle; and an electrical insulator surroundinga portion of the electrode body.
 13. The system of claim 12, wherein theelectrode body is formed of an electrically conductive, malleablematerial.
 14. The system of claim 12, wherein the electrical insulatoris configured to conform to the electrode body in the straight state andthe first bent state.
 15. The system of claim 1, wherein the shaft ofthe instrument comprises a joint adapted to permit the distal section ofthe shaft to move relative to the proximal section of the shaft.
 16. Thesystem of claim 15, wherein the joint is a ball bearing joint adapted toallow the distal section of the shaft to rotate relative to the proximalsection of the shaft.
 17. The system of claim 15, wherein the jointincludes a pin such that the joint allows the distal section of theshaft to swivel relative to the proximal section of the shaft.
 18. Thesystem of claim 15, further comprising a remote actuator configured toselectively control the joint.
 19. The system of claim 1, wherein theinstrument is adapted for sensing a depolarization wave.
 20. The systemof claim 1, wherein the grounding electrode is a needle electrode. 21.An ablation system comprising: an instrument including: an elongatedshaft defining a proximal section, a distal section, and an internallumen extending from the proximal section, wherein the distal sectionforms an electrically conductive rounded tip and defines at least onepassage fluidly connected to the lumen for distributing fluid from thelumen outwardly from the shaft, and further wherein the shaft is adaptedto be transitionable from, and independently maintain a shape in, astraight state and a first bent state, a non-conductive handle rigidlycoupled to the proximal section of the shaft, wherein an exteriorsurface of the shaft distal the handle and proximal the distal sectionis electrically non-conductive, a source of conductive fluid fluidlyconnected to the internal lumen; an energy source electrically connectedto the tip, wherein the energy source comprises ablation energy forcreating tissue lesions and stimulation energy for pacing the heart; anda switch coupled to the energy source, the switch configured to controldelivery of ablation energy and stimulation energy from the energysource to the tip of the instrument.
 22. The ablation system of claim21, wherein the delivery of ablation energy to the tip of the instrumentis stopped when the delivery of stimulation energy to the tip of theinstrument is started and the delivery of stimulation energy to the tipof the instrument is stopped when the delivery of ablation energy to thetip of the instrument is started.
 23. The ablation system of claim 21,wherein the switch is further coupled to the source of conductive fluid,the switch configured to control delivery of fluid from the source ofconductive fluid to the internal lumen of the instrument.
 24. Theablation system of claim 23, wherein the delivery of fluid to theinternal lumen of the instrument is stopped when the delivery ofablation energy to the tip of the instrument is stopped and the deliveryof fluid to the internal lumen of the instrument is started when thedelivery of ablation energy to the tip of the instrument is started. 25.The ablation system of claim 21, wherein the switch is a hand switch.26. The ablation system of claim 21, wherein the switch is a footswitch.
 27. The ablation system of claim 21, further comprising one ormore sensors located at the distal section of the instrument.
 28. Theablation system of claim 21, further comprising one or more indicatorlights located on the instrument and electrically connected to theenergy source, the indicator lights indicating the delivery of ablationenergy or stimulation energy.
 29. The ablation system of claim 21,wherein the tip is adapted to be dragged across tissue during anablation procedure, and further wherein in the first bent state, theshaft orients the tip so as to define a discernable drag direction, andin the straight state, the shaft is characterized by an absence of adiscernable drag direction.
 30. The ablation system of claim 21, whereinin the straight state, the shaft defines a linear axis, and furtherwherein in the first bent state, a portion of the shaft is deflectedrelative to the linear axis.
 31. The ablation system of claim 30,wherein the shaft is adapted to be transitionable to, and independentlymaintain a shape in, any direction relative to the linear axis.
 32. Theablation system of claim 21, wherein the shaft is adapted to betransitionable to, and independently maintain a shape of, a second bentstate different from the first bent state.
 33. The ablation system ofclaim 21, wherein the instrument is adapted for ablating heart tissuethrough a chest of a patient.
 34. The ablation system of claim 33,wherein the heart tissue is atrial tissue.
 35. The ablation system ofclaim 33, wherein the heart tissue is ventricular tissue.
 36. Theablation system of claim 33, wherein the instrument is adapted forablating heart tissue endocardially through a chest of a patient. 37.The ablation system of claim 33, wherein the instrument is adapted forablating heart tissue epicardially through a chest of a patient.
 38. Theablation system of claim 33, wherein the instrument is adapted forablating heart tissue transvascularly through a chest of a patient. 39.The ablation system of claim 21, wherein the instrument is adapted forstimulating heart tissue through a chest of a patient.
 40. The ablationsystem of claim 39, wherein the heart tissue is atrial tissue.
 41. Theablation system of claim 39, wherein the heart tissue is ventriculartissue.
 42. The ablation system of claim 39, wherein the instrument isadapted for stimulating heart tissue endocardially through a chest of apatient.
 43. The ablation system of claim 39, wherein the instrument isadapted for stimulating heart tissue epicardially through a chest of apatient.
 44. The ablation system of claim 39, wherein the instrument isadapted for stimulating heart tissue transvascularly through a chest ofa patient.
 45. The ablation system of claim 21, wherein the shaftincludes: an elongated electrode body forming the proximal section andthe distal section, the electrode body being directly coupled to thehandle; and an electrical insulator surrounding a portion of theelectrode body.
 46. The ablation system of claim 45, wherein theelectrode body is a tube formed of an electrically conductive, malleablematerial.
 47. A method of performing an ablation procedure, the methodcomprising: providing a first instrument including an elongated shaftand a handle, the shaft defining a proximal section rigidly coupled tothe handle, a distal section forming an electrically conductive tip;positioning the tip of the first instrument through a patient's chest;applying ablation energy to the tip of the first instrument whilecontacting cardiac tissue; creating an ablation lesion to isolate anarea of cardiac tissue; providing a second instrument including anelongated shaft and a handle, the shaft defining a proximal sectionrigidly coupled to the handle, a distal section forming an electricallyconductive tip; positioning the tip of the second instrument through apatient's chest; and applying stimulation energy to the tip of thesecond instrument while contacting the area of isolated cardiac tissueto assess transmurality of the ablation lesion.
 48. The method of claim47, wherein the first instrument further comprises an internal lumenextending from the proximal section of the shaft and in fluidcommunication with at least one passage formed in the distal section ofthe shaft.
 49. The method of claim 48, further comprising: dispensingconductive fluid from the internal lumen of the shaft via the at leastone passage.
 50. The method of claim 47, wherein the ablation energy isradiofrequency energy.
 51. A method of performing an ablation procedure,the method comprising: providing an instrument including an elongatedshaft and a handle, the shaft defining a proximal section rigidlycoupled to the handle, a distal section forming an electricallyconductive tip; positioning the tip through a patient's chest; applyingablation energy to the tip while contacting cardiac tissue; creating anablation lesion to isolate an area of cardiac tissue; stopping theapplication of ablation energy to the tip; repositioning the tip; andapplying stimulation energy to the tip while contacting the area ofisolated cardiac tissue to assess transmurality of the ablation lesion.52. The method of claim 51, wherein the instrument further comprises aninternal lumen extending from the proximal section of the shaft and influid communication with at least one passage formed in the distalsection of the shaft.
 53. The method of claim 52, further comprising:dispensing conductive fluid from the internal lumen of the shaft via theat least one passage while applying ablation energy to the tip.
 54. Themethod of claim 51, wherein the ablation energy is radiofrequencyenergy.
 55. A method of performing a left sided epicardial leadplacement procedure, the method comprising: providing an instrumentincluding an elongated shaft and a handle, the shaft defining a proximalsection rigidly coupled to the handle, a distal section forming anelectrically conductive tip; positioning the tip through a patient'schest to contact a first area of epicardial tissue of the patient's leftventricle; applying stimulation energy to the patient's right ventricle;recording the time at which a depolarization wave is sensed over theleft ventricle following stimulation of the right ventricle;repositioning the tip to contact a second area of epicardial tissue ofthe patient's left ventricle; reapplying stimulation energy to thepatient's right ventricle; recording the time at which thedepolarization wave is sensed over the left ventricle followingrestimulation of the right ventricle; placing an epicardial lead incontact with the area of tissue that had the longest time interval atwhich the depolarization wave was sensed over the left ventriclefollowing stimulation of the right ventricle.
 56. A method of performingan ablation procedure, the method comprising: providing an instrumentincluding an elongated shaft and a handle, the shaft defining a proximalsection rigidly coupled to the handle, a distal section forming anelectrically conductive tip; advancing the tip of the instrument througha patient's chest and into the patient's coronary sinus; positioning thetip of the instrument in the patient's coronary sinus between anexisting lesion encircling at least a portion of the patient's pulmonaryveins and the annulus of the patient's mitral valve; applying ablationenergy to the tip of the instrument while the tip is positioned in thecoronary sinus; and creating an ablation lesion in an area of cardiactissue surrounding the tip.